The present invention relates to a back light type liquid crystal apparatus.
In recent years, it is promoted to make a personal computer compact, and a portable device so called as a lap-top type widely spread. In this lap top type, a liquid crystal apparatus is generally employed for a display apparatus thereof, however, in accordance with a development to a color display in recent years, a back light type display apparatus in which a light source is arranged at the back of a liquid crystal display plate and a whole of a display surface is lighted up from a back side spread. It is necessary to make a brightness of the light source as the back light apparatus for this kind of display apparatus high, and light up the whole of the flat surface without unevenness of the brightness. In order to improve the brightness, an improved brightness can be easily achieved by increasing the brightness of the light source, however, an increase of the brightness of the light source is limited because a battery or the like is employed as a drive source in the lap-top type personal computer and the like, so that there has been conventionally no effective method.
As an edge light type light apparatus for a conventional liquid crystal display apparatus, there are apparatuses described in Japanese Patent Unexamined Publication Nos. 4-162002 and 6-67004. In these apparatuses, as shown in FIG. 2, a lamp such as a cold-cathode tube, a hot-cathode tube or the like is employed for a light source 1, this is arranged on an end surface of a light conductor plate 2 made of a permeable material, a light scattering layer 3 for scattering a light and a reflecting plate 4 for reflecting a light is provided on a lower surface of the light conductor plate 2, and a diffusion plate 5 made of a milk white synthetic resin having an optical confusion effect for making a brightness of the light surface uniform all around the whole surface is provided on an upper surface of the light conductor plate 2. Further, on an upper surface thereof, there are arranged a first light condensing plate 6 and a second light condensing plate 7 which converge a diffused light at a certain degree so as to improve a brightness of a front surface of the display apparatus.
Further, a structure of the light confusion layer for confusing the light guided by the light conductor plate 2 in a direction of the diffusion plate and a method of manufacturing the same are as follows. FIG. 3 shows a structure of the light confusion layer. The light confusion layer is structured such that a plurality of light confusion materials 8 using a titanium oxide or the like is formed on the surface of the light conductor plate 2 in accordance with a method such as a printing or the like. An optical strength from the light source becomes lowered as being apart from the light source 1. Accordingly, an area of the light confusion materials is set to become larger as they are apart from the light source.
On the contrary, as described in Japanese Patent Unexamined Publication No. 7-294745, there is proposed a light conductor plate of a type in which a grating groove is formed on a bottom surface of the light conductor plate so as to reflect an incident light to the light conductor plate.
As mentioned above, in the conventional light apparatus, it is structured such that an emitting light from the light source is introduced to the light conductor plate, confused by the light confusion materials contained in the light confusion layer and thereafter irradiated to a liquid crystal element after passing through the diffusion plate, so that the structure is complex and there is a problem that the brightness is lowered due to a loss such as the light confusion and the like. Further, there is a problem that in the method of forming the grating groove, it is hard to manufacture a metal mold.
In the conventional apparatus mentioned above, since a number of the elements is large and the diffusion plate and the light condensing plate are arranged on an upper surface of the light conductor plate, unevenness of the brightness can be reduced, however, there is a disadvantage that the whole brightness is reduced. In the case of this structure, since a uniformity of the brightness and an improvement of the brightness are always opposing objects, it is hard to solve them. On the contrary, in the case of the light conductor plate of the type in which the grating groove is formed, the improvement of the brightness can be achieved, however, it is significantly hard to manufacture the metal mold and make the brightness uniform.
The present invention is made for solving the current status mentioned above, and an object of the present invention is to provide a liquid crystal apparatus which improves the conventional disadvantages and can improve a brightness without increasing a brightness of the light source.
In order to achieve the object mentioned above, in accordance with the present invention, a light conductor plate having a plurality of small projecting portions or small recess portions (hereinafter, refer to as dots) with a suitably controlled angle of incline of a cross section is employed for converting a direction of a forward movement of a waveguide light within a light conductor plate into a predetermined direction. Further, a reflection film is formed along the dots or the reflection film is arranged as occasion demands. Further, a prism sheet having a suitable prism top angle is arranged as occasion demands, thereby irradiating a light beam having a suitable angle distribution toward a display element from a light outputting surface. Further, in order to prevent Moire from generating, a member in which an arrangement of the dots satisfies a fixed restricting condition and the dots are arranged and formed at random, is employed. Further, by changing a number of the dots and/or a shape thereof and/or a size thereof as occasion demands, an angle distribution of the emitting light is made uniform and an unevenness of the brightness is prevented from being generated.